The reaction proceeds in the presence of a suitable catalyst under pressure and at elevated temperature, 2-aminomethylpyridine initially being formed as an intermediate in the first step. The desired 2-aminomethyl piperidine is formed from the 2-aminomethylpyridine in a subsequent second hydrogenation step.
European patent 189,678 relates to the electrochemical reduction of 2-cyanopyridine to 2-aminomethylpyridine; it follows from U.S. Pat. Nos. 4,153,605 and 4,080,338 that the hydrogenation of 2-cyanopyridine by means of palladium/activated charcoal catalysts leads predominantly to .alpha.-bispicolylamine. 2-Aminomethyl piperidine, on the other hand, is formed only in minor amounts.
The conversion of 2-aminomethylpyridine to 2-aminomethylpiperidine by means of PtO.sub.2 catalysts in aqueous solution acidified with acetic acid is described in U.S. Pat. Nos. 3,772,230 and 3,631,046. However, the final working-up required--liberation of the amine with potassium hydroxide, extraction with diethyl ether, drying of the ether phase over sodium sulfate and fractional distillation--is very expensive.
Another process for the preparation of 2-aminomethylpiperidine forms the subject matter of Japanese Patents 86/251 663 and 86/251 659. According to the former, a solution of 2-cyanopyridine in benzene, with ammonia added, is hydrogenated to 2-aminomethylpyridine by means of Raney nickel. In a separate step, according to the latter reference, 2-aminomethylpyridine is converted to 2-aminomethylpiperidine with hydrogen in the aqueous phase in the presence of rhodium/activated charcoal as a catalyst. Because of the use of two different catalysts and the need to work in two different media--benzene solution on the one hand and aqueous phase on the other--the combined process is very laborious and impractical. Moreover, the final separation of the 2-aminomethylpiperidine from the aqueous solution formed involves considerable expense.
There is, therefore, a need for a process which avoids the disadvantages of the above-mentioned processes and which provides a method of hydrogenating 2-cyanopyridine to 2-aminomethylpiperidine using one and the same catalyst and without changing the solvent. The process should use a catalyst which is available in commercial quantities and should be able to be carried out at justifiable expense, even on an industrial scale. Furthermore, there should be the assurance that the reaction does not result in the formation of substantial amounts of by-products, but produces the desired useful product, namely 2-aminomethylpiperidine, in good yield.